Na ion - Ca 2 ion interactions were studied in aortic smooth muscle from normotensive (WKY) and hypertensive (SHR) rats. The aorta from SHR showed lower contractility to specific stimulus such as norepinephrine (NE) as well as to nonspecific stimulus such as high k plus depolarization. The lower contractility of SHR aorta to NE was not related to the alteration in alpha-adrenergic receptors since ED50 of NE in the two groups was not different. A decrease in (Na)ex caused an inhibition of NE induced contraction in both WKY and SHR groups. Alteration in (Na)ex from 0-140 mM also produced contraction by itself in both groups, the contractions being of higher magnitude in the SHR group. These observations indicate basic alteration in vascular contractility in the hypertensive state. Studies are in progress to relate these studies to Ca 2 ion fluxes.